Professor Roger Short of the University of Melbourne launched the 2002 project after learning that Mediterranean women capped their cervixes with sperm-souring citruses 300 years ago. “I wondered,” Short said, “could it work on HIV?”

Playing chef, he mixed a 20 percent lemon-juice solution with HIV positive semen in vitro. Within two minutes, the acidity cut HIV replication by 90 percent. Limes worked with equal zing.

The Thai Health Ministry agreed in May 2004 to back a two-year clinical trial. Short was elated. “If something as common as lemon/lime juice could be used for HIV prevention, it could help women without access to better methods.” Later this year, Thai participants will begin inserting lime-doused cotton balls before sex.

“This would be wonderful, but we’ll have to see what the trials reveal,” says Anna Forbes of the Global Campaign for Microbicides. “Microbicides can act differently in labs than in humans.” She also warns that acidity and anuses don’t mix—rectums are too sensitive.

Short is also planning to study 450 Nigerian sex workers—some of whom already douche with lemon juice. Pharma, though, has yet to unpeel any funding. “They know they can’t patent a fruit,” Short said, “so we’re looking elsewhere.”